Studies will be continued of the molecular mechanism of estrogen action and the role of receptor proteins in the process. Principal objectives are to determine molecular basis of the estrogen-induced transformation of the receptor that accompanies its translocation to the nucleus and to isolate and determine the structure and composition of both the cytoplasmic (4S) and nuclear (5S) forms of the receptor protein. Specific antibodies to both forms of the receptor protein are being prepared. BIBLIOGRAPHIC REFERENCES: E.V. Jensen, P.I. Brecher, M. Numata, S. Smith and E.R. DeSombre: Estrogen interaction with target tissues; two-step transfer of receptor to the nucleus. Hormones and Cyclic Nucleotides, J.G. Hardman and B.W. O'Malley, eds. Academic Press, New York, 1975, pp. 267-275. E.R. DeSombre, S. Mohla and E.V. Jensen: Receptor transformation, the key to estrogen action. J. Steroid Biochem. 6, in press (1975).